The present invention relates to the field of free wheel devices.
Free wheel devices generally comprise an outer ring equipped with a cylindrical interior slideway for cams of the free wheel, an inner ring or shaft equipped with a cylindrical exterior slideway for the said cams of the free wheel, a free wheel situated between the slideway of the outer ring and the slideway of the inner ring or of the shaft, and one or more members forming bearings which are intended to keep the outer and inner rings concentric and to transmit the radial forces between the said rings.
The bearings are in the form of a component of annular overall shape comprising a radial part in the shape of a roughly flat washer delimited by two circular rims to each of which an axial portion attaches.
The axial portions rest against corresponding bearing surfaces of the rings which may be an axial extension of the slideways, thus providing centring between the two rings by acting as plain bearings.
The free wheel comprises a single cage or a double cage consisting of two concentric cages, equipped with windows in which there are placed cams which, by jamming or by sliding between the two slideways, provide a one-way coupling between the outer and inner rings.
The cage generally comprises, at least on one side, a radial flank allowing the cage to be centred inside the corresponding bearing by coming into contact with one of the axial portions of a bearing.
The free wheel is thus capable of transmitting torque in one direction between the outer and inner rings and of allowing free rotation in the other direction.
To encourage the cams to pivot in the direction which encourages locking, there may be a spring which is in the form of a band exerting on each cam a return torque which tends to keep the cams permanently in contact with the slideways.
These devices are used, for example, in automatic transmissions for motor vehicles.
The conventional lateral bearings used for such free wheel devices are annular bearings of U-shaped cross section, it being possible for the said bearings to be produced by turning or by pressing metallic materials such as steel (turning) or alternatively copper-based alloys (the pressing of sheet brass, for example).
The two axial branches of the U constitute, via their cylindrical outer surfaces, the bearing surfaces for the sliding and centring of the said bearings on corresponding bearing surfaces of the inner and outer rings of the free wheel device.
These two axial branches are joined together by a radial portion constituting the strong web of the bearing and serving to transmit radial forces between the two rings.
The bearings are generally mounted with the branches of the U pointing towards the cage so that the said cage can be centred inside an axial branch of the bearing.
The centring function is thus fulfilled without increasing the axial size of the assembly.
A device of this type is known, for example, from patent FR 8509583 (Publication No. 2583843).
While such devices are entirely satisfactory, a number of problems are encountered in achieving accurate radial centring of the cage in the bearing.
Specifically, in the case of a single cage and conventional U-section bearings, the cylindrical annular part of the cage is located approximately mid-way between the axial branches of the bearing.
The result of this is that the height of the radial flank of the said cage has to be relatively great so that it can be centred inside the axial branch of the bearing, and this leads to a consumption of materials. The presence of these flanks increases the cost of materials and the weight.
On the other hand, the accuracy that can be obtained on the outside diameter of the radial flank using conventional cutting and pressing methods is limited and does not guarantee perfect centring of the cage in the bearing.
One consequence during operation may be the emergence of vibrational problems which are due to a lack of radial guidance of the cage in the bearing.
The object of the present invention is to overcome the disadvantages of the devices of the prior art.
The object of the present invention is to provide a free wheel device that is economic, lightweight and not very subject to vibrations.
The free wheel device according to the invention is of the type comprising an outer ring equipped with an interior slideway, an inner ring or shaft equipped with an exterior slideway, a free wheel placed between the slideway of the outer ring and the slideway of the inner ring and comprising a number of cams placed in windows of a cylindrical part of a single cage and providing a one-way coupling between the outer and inner rings, and at least one bearing placed radially between the outer and inner rings and intended to keep the said outer and inner rings concentric. At least a free end of the cylindrical part of the cage is centred radially on a cylindrical guiding bearing surface formed on the bearing adjacent to the said free end, the said cylindrical bearing surface being arranged so that it is coaxial with the slideways, approximately radially mid-way between the slideways.
In one embodiment of the invention, the cage consists in a single cylindrical portion.
In another embodiment of the invention, the cage includes a cylindrical portion and a radial portion capable of coming into contact with a cylindrical surface of another bearing.
In one embodiment of the invention, the cylindrical guiding bearing surface is formed by the edge of an annular groove formed in a radial part of the bearing.
In another embodiment of the invention, the cylindrical guiding bearing surface is formed by the edge of an annular shoulder formed in a radial part of the bearing.
In one embodiment of the invention, the bearing consists in a disc provided with bearing surfaces for sliding on the outer and inner rings.
In another embodiment of the invention, the bearing comprises a radial part and two cylindrical parts forming sliding bearing surfaces on the outer and inner rings, the cylindrical guiding bearing surface being placed on the radial part.
It is advantageous for the bearing or bearings to be made of sintered metal because of the relatively low manufacturing costs, the good accuracy of the bearings obtained and the very good friction properties on steel bearing surfaces of the rings and/or of the shaft. Specifically, the structure of the sintered metal, which is made up of a metal powder whose particles are bound together by compression and heating in a mould, encourages the retention of lubricant at the surface, and this greatly improves the lubrication at the contact surfaces.